Load bearing material

ABSTRACT

There is provided a load bearing material with a high energy-absorbing effect at the time of deformation. A metallic external tube  2,  a plurality of internal steel tubes  3, 3 A,  3 B arranged inside the external tube  2  are arranged by positioning the plurality of internal steel tubes  3, 3 A,  3 B, and thus, the load bearing capacity is improved by the plurality of the internal steel tubes  3, 3 A,  3 B. Further, when a load is applied, the internal steel tubes deform in a flattened form to thereby enable the external tube to deform as well. As a result, no stress concentrates locally on the external tube  2,  thus improving an energy-absorbing effect. Further, a filler  4  is filled between an inside  21  of the external tube  2  and outsides of the internal steel tubes, thereby enabling the plurality of the internal steel tubes  3, 3 A,  313  to be simply positioned.

TECHNICAL FIELD

The present invention relates to a load bearing material.

BACKGROUND ART

Heretofore, there have been known, as ones utilizing this type of a load bearing material, certain protective structures. The protective structures include guard structures against falling rocks, snow avalanche, collapsed earth and sand, or the like, such as a guard fence comprising supporting posts provided at given intervals, horizontal ropes provided between each of the supporting posts to thereby shield spaces between the supporting posts with wire nets fastened to the horizontal ropes (e.g., refer to patent document 1); another guard fence including multistage horizontal rods made of concrete, metal or the like, provided between each of supporting posts; yet another guard fence employing supporting posts set up on a slope face at given intervals to spread a guard net between the supporting posts, said supporting posts having their lower ends mounted on the slope face, and held in position by coupling anchors provided on the slope face with the lower portions of the supporting posts, using fixing ropes (e.g., refer to patent document 2); and a suspension-type guard fence in which the anchors and the upper and lower portion's of the supporting posts are coupled together, using fixing ropes (e.g., refer to patent document 3), and it is noted that steel tubes are employed for these supporting posts.

Also, there is known another protective structure which comprises a revetment formed on a slope face, main structural members each of which is inserted into the ground after penetrating the revetment while a portion thereof protruded from the revetment is supported in a cantilevered manner, and a floor slab provided between the main structural members protruded from the revetment (e.g., refer to patent document 4), in which steel tubes are employed as the main structural members.

As described above, a steel tube is employed as the members of a protective structure. Also, there have been known other protective structures using steel tubes, such as the one in which a supporting post of a rock fall prevention fence is manufactured by arranging unbonded type PC steel materials coated with a sheath member, and then filling concrete into steel tubes (e.g., refer to patent document 5); and the one in which a filler is filled into a respective interior of a double steel tube, and cement milk or mortar is employed as the filler (e.g., refer to patent document 2). Related art documents

Patent document 1: Japanese unexamined patent application publication No. 6-173221

Patent document 2; Japanese unexamined patent application . publication No. 2000248515 (paragraph 0013)

Patent document 3; Japanese unexamined patent application publication No. 8.184014

Patent document 4; Japanese unexamined patent application publication No. 2001.323416

Patent document 5: Japanese unexamined patent application publication No. 6.146225

Patent document 6: Japanese unexamined patent application. publication No. 9-203036

DISCLOSURE OF THE INVENTION

Problem to be solved by the Invention

As described in the above patent documents, an infilled steel tube filled with concrete therein can be improved in rigidity as compared with a hollow one.

When the infilled steel tube is subjected to a load such as an impulsive force or the like and thus a distortion is generated in the pipe by a bending moment, however, there occur such problems that deformation hardly occurs in a cross section of the infilled pipe while the tensile strength of concrete is low on its cross-sectional side subjected to a tensile stress and hence fracture is easy to occur in the steel tube, and that when the fracture occurs at an early stage, reduction of an energy-absorbing efficiency of the steel tube is resulted, as well as drastic decrease in a load-load bearing capacity thereof.

Further, there arises another problem that even if distortion occurs within the elasticity of a steel tube, a crack occurs on a side where tensile stress is applied and hence even after removing a load, the distortion is likely to remain due to plastic deformation, thus resulting in a decrease in a load load bearing capacity.

Therefore, it is an object of the present invention to provide a load bearing material having a high energy-absorbing efficiency at the time of its deformation.

Mean for solving the Problem

According to the present invention, there is provided a load bearing material including a metallic external tube and a plurality of metallic internal tubes arranged inside said metallic external tube with said plurality of metallic internal tubes positioned therein, wherein said external and internal tubes have a circular cross-section, and when a plastic deformation takes place due to a bending moment, the internal tubes are allowed to deform in a flattened form.

Also, according to the present invention, the load bearing material is provided with three or more internal tubes.

Also, according to the load bearing material of the present invention, there is provided a positioning means for positioning said plurality of internal tubes, said positioning means being provided as a filler filled between an inner surface of said external tube and outer surfaces of said internal tubes.

Also, according to the load bearing material of the present invention, steel tubes are employed as the external and internal tubes,

Also, according to the present invention, the internal tubes are thinner than the external tube in tube wall thickness,

Also, according to the present invention, a cement-based filler is employed as the filler.

Also; according to the present invention, the outer surfaces of the internal tubes are arranged close to one another.

Also, according to the present invention, the outer surface of each internal tube is positioned close to other internal tubes at two or more places.

Also, according to the present invention, the plurality of the internal tubes are arranged in a manner that the outer surfaces thereof are positioned close to one another, while other internal tubes are arranged inside regions surrounded by the internal tubes.

Also, according to the present invention, the outer surfaces of some of the internal tubes are positioned close to those of other internal tubes at six or more places.

Also, according to the present invention, two or more of the internal tubes are arranged substantially in parallel with a centerline of a cross section of the external tube inside the external tube.

Also, according to the present invention, three or more of the internal tubes are arranged substantially in parallel with the centerline of the cross section of the external tube.

Effects of the invention

According to the conventional infilled steel tube, a crack occurs in the inside filler, and its cross-sectional deformation is impossible due to the outside tube being restrained by the inside filler, thus posing the problem that stress is concentrated locally on a part of the cross section of the steel tube. For the purpose of solving the problem, the inventers applied. themselves close to the studies of the problem., thus having arrived at the present invention.

According to the scheme described above, the load bearing capacity is improved by the plurality of the internal tubes, and besides when subjected to a load, the internal tubes deform plastically in their cross sections in a: flattened form, Accordingly, the external tube also becomes plastically deformable, thus improving an energy-absorbing effect without stress being concentrated locally on the external tube.

Further, the three or more internal tubes are provided, and hence, the energy-absorbing effect is improved as compared with the conventional load bearing material.

Furthermore, the filler is employed as a positioning means. Hence, a plurality of the internal tubes can be simply positioned by filling the filler into the external tube.

Moreover, a steel tube is employed for the external and internal tubes, and the steel tube has a tenacious property. Hence, even if deformed, abrupt deterioration of the load bearing capacity of the tube can be prevented and a stable energy-absorbing effect can be obtained.

Besides, the internal tubes are thinner than the external, tube. Hence, the internal tubes having a smaller diameter become easily deformable in a flattened form.

Further, a cement-based filler is employed as the filler. A moderate price as well as easiness in handling are realized.

Furthermore, the internal tubes are arranged close to one another, and thus when a load is applied, the internal tubes contact with one another to deform in relation to one another. Hence, energy can be absorbed.

Moreover, the outer surface of each internal tube is positioned close to other internal tubes at two or more positions so that it is contacted by other internal tubes at both sides thereof. Hence, when a load is applied to the load bearing material, they are allowed to mutually deform to enable energy to be absorbed.

Besides, said plurality of the internal tubes are arranged in a manner that the outer surfaces thereof are positioned close to one another to thereby define regions surrounded by some of said internal tubes, while other internal tubes are arranged inside said regions. Hence, when a load is applied to the load bearing material, they are allowed to mutually deform to enable energy to be absorbed.

Further, the outer surfaces of said internal tubes are positioned close to those of other internal tubes at six or more places. Hence, when a load is applied to the load bearing material, they are allowed to mutually deform to enable energy to be absorbed. Specifically, in the case of using the internal tubes with the same diameter, they are arranged in such a manner that one tube may be arranged close to other six tubes. Hence, the most efficient arrangement of the tubes can be realized.

Furthermore, two or more of said internal tubes are arranged substantially in parallel with a centerline of a cross section of said external tube inside said external tube, and thus, the load bearing material is employed so that the plurality of the internal tubes thus arranged may be positioned in a region upon which a tensile force acts when the load bearing material is subjected to a load, .thus making it possible to resist the tensile force through the internal tubes.

Moreover, three or more internal tubes are arranged substantially in parallel with the centerline of the cross section of the external tube. Hence, the three or more internal tubes can effectively withstand the tensile force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a first embodiment of the present invention.

FIG. 2 is a front elevation of a load bearing material according to the first embodiment of the present invention, said load bearing material being employed for an experiment.

FIG. 3 is an explanatory view showing the result of the experiment made on the first embodiment of the present invention.

FIG. 4 is a graph ,illustrating a relationship between bending moment and rotation angle in a loaded position in the first embodiment of the present invention.

FIG. 5 is a graph illustrating a relationship between a displacement in the loaded position. and an absorbed energy in the first embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating a second embodiment according to the present invention.

FIG. 7 is a cross-sectional view illustrating a third embodiment according to the present invention.

FIG. 8 is a cross-sectional view illustrating a fourth embodiment according to the present invention.

FIG. 9 is a cross-sectional view illustrating a fifth embodiment according to the present invention.

FIG. 10 is a cross-sectional view illustrating a sixth embodiment according to the present invention.

FIG. 11 is a cross-sectional view illustrating a seventh embodiment according to the present invention.

FIG. 12 is a cross-sectional view illustrating an eighth embodiment according to the present invention.

FIG. 13 is a cross-sectional view illustrating a ninth embodiment according to the present invention,

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder is a detailed description of preferred embodiments according to the present invention with reference to the appended drawings.

Embodiment 1

Next is a description of a first embodiment according to the present invention with reference to FIG. 1 to FIG. 5. As shown in FIG. 1, a load bearing material. 1 is provided with an external tube 2 made of a steel tube, internal tubes 3, 3A, 3B, . . . constituting a plurality of metallic internal tubes arranged inside the external tube 2, and a filler 4 filled, as a positioning means, between an inner surface 21 of the external tube 2 and outer surfaces 31 of the internal steel tubes 3. All the internal steel tubes 3, 3A, 3B, . . . are formed to have the same structure and generally thinner than, the external tube 2 in tube wall thickness. Alternatively, a spacer or the like may be employed as such positioning means. Otherwise, the internal steel tubes 3, 3A, 3B, . . . may be arranged substantially densely within the external tube 2 by suitably selecting the diameters of the internal steel tubes 3, 3A, 3B, . . . , whereby the internal tubes 3, 3A, 3B, . . . themselves each act as a positioning means.

The external tube 2 and the internal steel tube 3 are circular in cross section and are hollow. The plurality of the internal steel tubes 3, 3A, 3B, . . . , having the same diameter are arranged close to one another in a nearly hexagonal honeycomb shape so that the outer surfaces 31 of these internal steel tubes 3, 3A, 3B, . . . may come in contact with one another. Specifically, in the center of the external tube 2 is arranged one internal steel tube 3, and then six inner steel tubes 3A are arranged so as to contact with the outer surface 31 of the central inner steel tube 3, with the adjacent internal steel pipes contacting with each other. Accordingly, the central internal steel tube 3 is allowed to contact with the six internal steel pipes 3A, so that the central internal steel tube 3 is positioned inside a region surrounded by these six internal steel pipes 3A.

Further, twelve inner steel tubes 3B are arranged in a manner surrounding the six inner steel tubes 3A, with the adjacent internal steel pipes 3B contacting with each other. Three of the internal steel pipes 3B are arranged in parallel with a cross-sectional centerline S passing through the center of the external tube 2, with the internal steel tube 3B in the middle position contacting with the two internal steel pipes 3A, while the internal steel pipes 3B at both sides contacting with one internal steel tube 3A, respectively.

Accordingly, each internal steel tube 3A is arranged close to the six tubes consisting of the internal steel tube 3, the adjacent two internal steel tubes 3A and the three internal steel tubes 3B. Also, as described above, among the juxtaposed three internal steel tubes 3B, the central steel tube 3B contacts with the four internal steel tubes, i.e., the two internal steel tubes 3A and the internal steel tubes 3B on both ends, while the internal steel tubes 3B on both sides arc each allowed to contact with the three internal steel tubes, i.e., the one internal steel tube 3A and the adjacent two internal steel tubes 3B. According tri the present embodiment, the outside diameter of each of the inner steel tubes 3, 3A, 3B, 3C is less than or equal to one fifth of the external tube 2.

According to the present embodiment, insides of the internal steel tubes 3, 3A, 3B are made hollow so as to be deformable. Such hollowness enables the load bearing material 1 to be lightweight. The hollowness achieved by filling no filler therein, however, is not necessarily required but some filler may be filled therein as long as they are deformable. In other words, the internal steel tubes 3, 3A, 3B may be either hollow or filled with a deformable filler. As such deformable filler, a filler more flexible than. at least the internal steel tubes 3, 3A, 3B should be employed.

As for the filler 4 employed as a positioning means, a cement-based filler, for example, may be employed, such as mortar, concrete or the like. In addition to those, various types of fillers may be employed if they are solidified or shaped with time.

Also, as shown in FIG. 2, the load bearing material 1 may he used as a supporting post, for example, said supporting post having its lower portion buried in and fixed to the ground G and its upper portion protruded from the ground. A plurality of the pasts are allowed to stand on the ground G at intervals and can be used for a rock fall prevention guard fence by shielding spaces between the plurality of the posts by means of nets.

Next is a description of a working example of the invention that was actually tested. As for the material under test, the working example was a steel pipe including the external tube 2 having an outside diameter of 318.5 mm and a thickness of 6.0 mm and the internal steel tubes 3, 3A, 3B having an outside diameter of 60.5 mm and a thickness of 3.2 mm, and mortar, used as the filler. For a comparative example was employed an infilled steel tube including a steel tube having an outside diameter of 318.5 mm and a thickness of 6.0 mm, which was filled with mortar without providing any internal steel tubes.

Each of the external and internal tubes 2, 3 was 6 m in length. Both ends of the external tube 2 were provided with a cover 101, and mortar was filled from a filling hole 102 bored in the external tube 2, respectively.

FIG. 4 is a graph showing the result of the test obtained by applying a load F to the central portions of the working example and the comparative example with both ends thereof being supported. In the graph, the axes of ordinate and abscissa indicate a moment at a load point and a rotation angle 0 at the load point, respectively. As shown on the left side in the graph, it proved that the working example had a wider range of proportional change and a higher load bearing capacity.

Further, it was confirmed that the working example indicated an elastically deformable range of up to about 400 kN-m, while the comparative example indicated that of up to about 200 kN-m, causing plastic deformation. to occur when the load F exceeded that level, which means that when the load exceeding 200 kN-m is applied to the comparative example, distortions due to plastic deformation remain even if the load is removed, and then, when a load is applied again due to rock fall or the like, the comparative example exhibits a lower load bearing capacity than initially designed. Contrarily, the working example has the wider elastically deformable range and therefore, even if a load is applied again after the load of about 200 KN-m is applied and then removed, reliability in load bearing capacity remains high in the working example. This is due to the fact that when bending occurs in the infilled tube, it gives rise to crack in mortar acting as a filler, in a region where tensile force exerts, and even if the load is removed, the strength obtained by mortar is no longer available.

Also, in FIG. 4, an amount of energy absorption corresponds to an area surrounded with the abscissa axis indicating zero moment and a curve in the graph. Thus, it is demonstrated therefrom that the working example has an extremely large area as compared with the comparative example, and that the comparative example is broken at a rotation angle of about 22 degrees, while the working example is not broken even if the rotation angle exceeds 35 degrees, proving that the working example is excellent in energy absorption efficiency.

FIG. 5 is a graph where the abscissa and ordinate axes indicate a displacement at the load point and absorbed energy, respectively, demonstrating that the working example exhibits a lager absorbed energy than that of the comparative example.

Next, a difference in amount of energy absorption between the working example and the comparative example is studied. The reason why the energy absorption of the. working example becomes larger than that of the comparative example is that in the comparative example, a crack is not only produced in mortar to decrease the strength but the cross-sectional deformation of the external steel tube 2 is restricted by the mortar; in other words, the external tube 2 is unable to deform in a flattening direction and thus stress is concentrated on a cross section on a side where tensile strength exerts to thereby cause a breaking therefrom. According to the working example, however, the internal tubes are allowed to deform in a flattened form to absorb energy, and besides the external tube 2 is also capable of flatly deforming in its cross section, permitting energy to be effectively absorbed as a whole, as shown in FIG. 3. In addition, the external tube 2 and the internal tubes 3, 3A, 3B are allowed to deform in such a manner that their cross-sectional shapes get narrowed in the direction of the application of load F but get broadened in the direction perpendicular to the direction of the application of the load F. Besides, according to the conventional double steel tube filled with a filler (not shown), a deformable amount of an interior steel tube is small, whereas, according to the internal tubes 3, 3A, 3B of the working example of the present invention, they are collapsed such that upper and lower central portions in the diametrical direction come closer to each other, or so as to be co-shaped, and hence, the internal tubes 3, 3A, 3B in the working example proves to be large in deformable amount, thus indicating the larger energy absorption amount. Moreover, whilst an outer part of the cross section of the tube that is subjected to tensile or compressive force is substantially deformed in a normal case, but the internal tube 3 in the center is allowed deform to enable energy to be absorbed, due to the plurality of the internal tubes 3, 3A, 3B being densely arranged.

In this case, when a bending moment is generated in the load bearing material 1, the adjacent internal tubes 3, 3A, 3B contact with one another and thus are allowed to deform, while they are also deformed through the filler 4 between the internal tubes 3, 3A, 3B. Hence, it is more preferable that the spaces between the internal tubes 3, 3A, 3B be filled with the filler rather than allow them to remain hollow.

When an ordinary steel tube is locally buckled, flexural capacity is extremely lowered. In order to prevent this lowering, there exists an infilled steel tube filled with concrete. Lowering of the flexural capacity can be prevented as a result of the collapsing of a cross-sectional shape in this infilled steel tube. Nevertheless, when deformation due to the collapsing proceeds, the concrete filled inside the infilled tube is not deformable, and hence, distortions concentrate on the exterior tube to thereby break the steel tube, accompanied by a brittle fracture.

On the other hand, according to the load bearing material 1 of the present embodiment, even if the cross-sectional shape of the external tube 2 provided with the internal tubes 3, 3A, 3B therein deforms by bending force to collapse, the lowering of the load bearing capacity can be restrained. Further, the load bearing material 1 of the present embodiment has such a feature as being free from local concentration of distortions on the exterior tube 2 by the collapse of the internal tubes 3, 3A, 3B, This mechanism is resulted from the fact that a steel material itself has a tenacious property and if the cross-sectional shape collapses to cause a change in cross-sectional performance, no abrupt lowering of load bearing capacity occurs, Besides, due to the change in the cross-sectional shape of the load bearing material 1, it can exert a substantial energy absorption performance. In addition, the external tube 2 and the internal tubes 3, 3A, 3B deform in such a manner as to change their cross-sectional shape from the circular one to the vertically-shortened and horizontally-elongated one. For example, the deformation occurs so that the vertical length thereof becomes 65% or less, preferably 60% or less of the horizontal length thereof. In this case, at least one of the internal tubes 3, 3A, 3B may deform within this range of deformation.

As described in the present embodiment, corresponding to the claims, there is provided the load bearing material in which the metallic external tube 2, the internal tubes 3, 3A, 3B, comprising the plurality of metallic internal tubes, arranged inside the external tube 2 are included and then the plurality of the internal tubes are each positioned; and in the load bearing material, the external tube 2′and the internal tubes 3, 3A, 3B are circular in cross section and when plastic deformation occurs due to a bending moment caused by a force greater than a given level, the internal tubes 3, 3A, 3B are allowed to deform in a flattened form. Hence, the load bearing capacity of the load bearing material is improved by the plurality of the internal tubes 3, 3A, 3B and besides when a load is applied, the internal tubes 3, 3A, 3B deform in a flattened form, which in turn makes it possible to have the external tube 2 deform as well, thus improving the energy-absorbing efficiency without stress being concentrated locally on the external tube 2.

Further, as described in the present embodiment, corresponding to claim, the three or more internal tubes are provided. Hence, the energy-absorbing effect is improved as compared to the conventional load bearing material.

Furthermore, as described in the present embodiment, corresponding to claim, the filler 4 filled. between the inner surface 21 of the external tube 2 and the outer surfaces 31 of the internal tubes 3, 3A, 33 is allowed to act as a positioning means for positioning the plurality of the internal tubes 3, 3A, 3B. Hence, by filling the external tube 2 with the filler 4, the plurality of the internal tubes 3, 3A, 3B can be easily positioned.

Moreover, as described in the present embodiment, corresponding to claim, the external tube 2 and the internal tubes 3, 3A, 3B are steel tubes, having a tenacious property, and thus even if they are deformed, the abrupt lowering of the load bearing capacity can be prevented.

Besides, as described in the present embodiment, corresponding to claim, the internal tubes 3, 3A, 38 are formed thinner than the external tube 2 in tube wall thickness. Hence, the internal tubes 3, 3A, 33 with small diameter become easily deformable.

Further, as described in the present embodiment, corresponding to claim, the cement-based filler is used as the filler 4. Hence, the load bearing material 1 becomes inexpensive and easy to handle.

Furthermore, as described in the present embodiment, corresponding to claim, the outer surfaces 31 of the internal tubes 3, 3A, 3B are arranged so as to be adjacent to one another. Hence, when a load is applied, the internal tubes 3, 3A, 3B, come in contact with one another to deform, thus permitting energy to be absorbed.

Moreover, as described, in the present embodiment, corresponding to claim, the outer surfaces 31 of the internal tubes 3, 3A, 38 come close to other tubes at two or more positions to cause the internal tubes 3, 3A, 3B to come in contact with the other tubes from both sides thereof. Hence, when a lead is applied, the internal tubes mutually deform, thus permitting energy to be absorbed.

Besides, as described in the present embodiment, corresponding to claim, within a region surrounded by the plurality of the internal tubes 3B arranged so that the outer surfaces thereof are positioned close to one another, the other internal tubes 3, 3A are arranged. Hence, when a load is applied, the internal tubes 3, 3A mutually deform, thus permitting energy to be absorbed.

Further, as described in the present embodiment, corresponding to claim, the outer surfaces of the internal tubes 3, 3A are positioned close to the other internal tubes 3, 3A, 3B at six or more positions. Hence, when a load is applied and the internal tubes 3, 3A, 3B come in contact with one another, the internal tubes 3, 3A are allowed to mutually deform, thus permitting energy to be absorbed. Besides, when the tubes are of the same diameter, the one internal tube 3 can be arranged adjacently to the other six internal tubes 3A, thus realizing the most efficient arrangement.

Furthermore, as described in the present embodiment, corresponding to claim, inside the external tube 2, the plurality of the internal tubes 3, 3A, 3B are arranged substantially in parallel with the centerline of the cross section of the external tube 2. Specifically in this embodiment, the two internal tubes 3A arc arranged in parallel, and the three internal tubes 3B are arranged in parallel as well. Hence, by employing the load bearing material 1 with the plurality of the internal tubes 3A, 3B arranged in parallel being positioned in a region where tensile force acts at the time of application of a load, it is possible to withstand the tensile force through these internal tubes 3A, 3B.

Moreover, as described in the present embodiment, corresponding to claim, three or more internal, tubes 3B are arranged substantially in parallel with the centerline of the cross section of the external tube 2. Hence, the three or more internal tubes 3B can withstand efficiently the tensile force.

In addition to the foregoing, as an effect specific to the present embodiment, the plurality of the internal tubes 3, 3A, 3B are densely arranged in honeycomb geometry with no space therebetween, and hence, by providing the internal tubes 3, 3A, 3B arranged in honeycomb geometry, load bearing capacity and an energy-absorbing effect are allowed to be excellent.

Embodiment 2

FIG. 6 shows a second embodiment of the present invention and the same symbols are used for parts the same as in the first embodiment and then the detailed description is given with the description of the same part omitted. According to this embodiment, there are arranged, inside the external tube 2, the central internal steel tube 3 and the six internal steel tubes 3A surrounding the internal tube 3, and then the filler 4 is filled in the external tube 2. The internal steel tubes 3, 3A are arranged approximately densely. Besides, in this embodiment, the outer diameter of the internal tubes 3, 3A is less than or equal to one third of that of the external tube 2.

As described above, according to this second embodiment, the same function and effect are exerted as those done in the first embodiment. Particularly in this second embodiment, the two internal tubes 3A are arranged substantially in parallel with the centerline S of the cross section of the external tube 2.

Embodiment 3

FIG. 7 shows a third embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, the external tube 2 has a smaller diameter as compared to that in the second embodiment, or otherwise, the internal tubes 3, 3A have a larger diameter so that the internal tubes 3A substantially come in contact with the external tube 2, thereby positioning a plurality of the internal tubes 3, 3A. In addition,, the outer diameter of the internal tubes 3, 3A is less than or equal to one third of that of the external tube 2.

As described above, according to the third embodiment, the same function and effect are exerted as those done in the above embodiments. In this third embodiment, the two internal tubes 3A are arranged substantially in parallel with the centerline S of the cross section of the external tube 2. Besides, the internal tubes 3A are arranged so as to substantially contact with the external tube 2, thereby positioning the plurality of the internal tubes 3, 3A, which, in this case, act as a positioning means themselves.

Embodiment 4

FIG. 8 shows a fourth embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, four internal tubes 3A are arranged at portions corresponding to vertices of a quadrate and the internal tubes 3A, 3A are arranged substantially in parallel with the centerline S of a cross section of the external tube 2, thus exerting the same function and effect as those in each of the above embodiments. In addition, the outer diameter of the internal tubes 3A is less than or equal to half that of the external tube 2.

Embodiment 5

FIG. 9 shows an fifth embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, three internal tubes 3A are arranged at positions corresponding to the vertices of a triangle, thus exerting the same function and effect as those in each of the above embodiments. In this embodiment, the outside diameter of the internal steel tubes 3A is less than or equal to half of that of the external tube 2.

Embodiment 6

FIG. 10 shows an sixth embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, the internal tube 3 is not used under, the configuration of the first embodiment, and instead, the filler 4 is filled in the center, thus exerting the same function and effect as those in each of the above embodiments.

According to this embodiment, the internal tube 3 in the center of the external tube 2 is omitted. This center acts as a central axis for compression and tension when a bending load is applied, and therefore, in a situation prior to an impact load being applied, it gives few advantages to increasing strength to provide the internal tube 3 in the external tube 2, and thus omitting the internal tube 3 leads to reduction in material cost.

Embodiment 7

FIG. 11 shows an seventh embodiment of the present invention and the same symbols are used. for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, the central internal tube 3 and the six internal tubes 3A surrounding the same are not used under the configuration of the first embodiment, and instead, the filler 4 is filled in the center and the internal tubes 3A arc arranged in an substantially close manner, thus exerting the same function and effect in each of the above embodiments.

According to this embodiment, the seven internal tubes 3, 3A located nearer to the center are omitted. When the load bearing material 1 is bent, however, parts where comparatively large tensile stress and compressive stress are applied are outer areas in the cross section and therefore, the strength can be effectively improved by arranging the internal tubes 3B close to each other in these parts.

Embodiment 8

FIG. 12 shows an eighth embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, none of the six internal tubes 3A is used under the configuration of the first embodiment, and instead, the filler 4 is filled and the internal tubes 3A are arranged in an substantially close manner, thus achieving the same function and effect as those in the above embodiments.

Further, according to this embodiment, before the filler 4 is filled, the outside internal tubes 3B can be temporarily fixed by a temporarily-fixing jig not shown with reference to the internal tube 3 in the center, thus leading to the easiness in manufacturing the load bearing material 1.

Embodiment 9

FIG. 13 shows a ninth embodiment of the present invention and the same symbols are used for parts the same as in each of the above embodiments and then the detailed description is given with the description of the same part omitted. In this embodiment, no central internal tube 3 is used under the configuration of the second embodiment, and instead, the filler 4 is filled in the center, thus exerting the same function and effect as those in the above embodiments.

In the meantime, the present invention is not limited to the above embodiments and various modifications are possible. In the above embodiments, the examples are shown where steel tubes are employed as the external and internal tubes, but they may be made of other materials than iron, such as aluminum, stainless steel and alloys of these metals, and tubes made of various metals may also be used. Although the cement-based material is employed as the filler in the above embodiments, a foamed material such as foam polystyrene resin that is foamed in-situ or the like may be filled to position the internal tubes. Since the foaming material is deformable with comparatively small force and hence may be filled in the internal tubes. Further, although in the above embodiments, the internal tubes with the same diameter and the same tube wall thickness are employed, tubes with different tube wall thicknesses and different diameters may be combined. Furthermore, the outer surface of the external tube is not necessarily exposed to the outside but the load bearing material according to the present invention may be employed, for example, as a steel tube inside a double steel tube.

DESCRIPTION OF SYMBOLS

1 load bearing material

2 external tube

21 outer surface

3, 3A, 3B internal steel tubes (internal tubes)

4 filler (positioning means) 

1. A load bearing material including a metallic external tube and a plurality of metallic internal tubes arranged inside said metallic external tube with said plurality of metallic internal tubes positioned therein, wherein said external and internal tubes have a circular cross-section, and when a plastic deformation, takes place due to a bending moment, the internal tubes are allowed to deform in a flattened form.
 2. The load bearing material according to claim 1, wherein said load. bearing material is provided with three or more internal tubes.
 3. The load bearing material according to claim 1, wherein a positioning means for positioning said plurality of internal tubes is a filler filled between an inner surface of said external tube and outer surfaces of said internal tubes.
 4. The load bearing material according to claim 2, wherein a positioning means for positioning said plurality of internal tubes is a filler filled between an inner surface of said external tube and outer surfaces of said internal tubes.
 5. The load bearing material according to claim 1, wherein steel tubes are employed as said external tube and said internal tubes.
 6. The load bearing material according to claim 3, wherein steel tubes are employed as said external tube and said. internal tubes.
 7. The load bearing material according to claim 1, wherein said internal tubes are thinner than said external tube in tube wall thickness.
 8. The load bearing material according to claim 3, wherein said internal tubes are thinner than said external tube in tube wall thickness.
 9. The load bearing material according to claim 3, wherein a cement-based filler is employed as said filler.
 10. The load bearing material according to claim 1, wherein the outer surfaces of said internal tubes are arranged close to one another.
 11. The load bearing material according to claim 3, wherein the outer surfaces of said internal tubes are arranged close to one another.
 12. The load bearing material according to claim 10, wherein the outer surface of each internal tube is positioned close to other internal tubes at two or more places.
 13. The load bearing material according to claim 10, wherein said plurality of the internal tubes are arranged in a manner that the outer surfaces thereof are positioned close to one another to thereby define regions surrounded by some of said internal tubes, while other internal tubes are arranged inside said regions.
 14. The load bearing material according to claim 12, wherein the outer surfaces of said internal tubes are positioned close to those of other internal tubes at six or more places.
 15. The load bearing material according to claim 12, wherein two or more of said internal tubes arc arranged substantially in parallel with a centerline of a cross section of said external tube inside said external tube.
 16. The load bearing material according to claim 15, wherein three or more of said internal tubes are arranged substantially in parallel with the centerline of the cross section of said external tube. 